This invention relates generally to the diagnosis and assessment of treatment of visual disorders by objective means. More specifically it relates to the determination of extent and magnitude of local defects in the visual field of the eye by simultaneous stimulation of a large number of locations on the retina and analysis of the elicited electrical signals derived from the eye (electro-retinogram or ERG) or the scalp (visual evoked cortical response or VECR).
Most pathologies of the human visual system do not affect the entire visual field equally, but begin in small patches which then may grow into larger field defects. The locations of those patches on the retina are often a characteristic of the disease. The detection and determination of the size of such defects is thus of great importance not only for diagnosis, but also for the assessment of treatment. The techniques currently used in the clinic for this purpose are psychophysical in nature i.e., they require a judgement and response from the patient. They are thus subjective and often difficult to use, especially with very young or old patients, or persons who for other reasons are unable to adequately perform the task. The most popular techniques for retinal "mapping" or debut location determinates are known under the names "tangent screen" or "perimetry". More or less automated equipment for performing perimetry is commercially available from companies such as Goldman, Baush and Lomb, Coopervision, and others. The process of obtaining visual field plots with such equipment is usually lengthy, laborious (if not for the operator then always for the patient) and produces results which are not always reliable. Objective bioelectrical signals are currently obtained and used in the clinic, to obtain global responses from the entire visual field or a large segment thereof. The usefulness of smaller stimuli (focal ERG and VECR) has been demonstrated most notably by Sandberg and Berson and by Hirose et al. However, the techniques introduced by these authors only permit testing of one location at a time. Application of their technique for the purpose of objective perimetry was heretofore thought not feasible for two reasons: sequential testing of a large number of retinal location is much too time consuming for clinical applications, and comparison of signals obtained sequentially from different locations is unreliable because of temporal variations in signal-to-noise ratio. A different approach has recently been presented at the annual meeting of the Association for Research in Vision and Opthamology (ARVO). In the approach, each location of the retina is stimulated with a signal of a different frequency. However this imposes theoretical as well as practical limitations on the number of locations which can be simultaneously tested. While these investigators hope to be able to test up to 64 locations, they are currently testing only 8 or 16 locations.
The present invention overcomes those limitations by the simultaneous stimulation of a large number of locations. Acceptable results are obtained in times feasible in the clinic (10 to 20 minutes) and artifactual noise, such as produced by blinks, affects all focal responses the same or to a similar degree.
In carrying out the invention a matrix of independently controllable optical elements is placed in the field of view of the patient. A special class of binary sequences, called M-sequences, is utilized in electronically activating the elements. M-sequences are discussed in Golomb, Shift Register Sequences, 1982, Aegean Park Press, Laguna Hills, Calif.
The present invention permits the testing of a much larger number of locations. Currently 256 are used, but an increase to 2000 or more is feasible without extending the length of the procedure.
Various types of focal stimulation can be used with the present invention such as local flash and local pattern reversal color alternation. The most appropriate mode of stimulation depends on the pathology at hand.
The invention and objects and features thereof will be more readily apparent from the following detailed description and appended claims when taken with the drawings, in which: